1. Field of the Invention
The invention relates to a voltage regulator, and more particularly to a voltage regulator coupled to a startup circuit, where the latter initiates the voltage regulator and disconnects itself from the voltage regulator when the voltage regulator has reached its desired final output voltage.
2. Description of the Related Art
To increase the Power Supply Rejection Ratio (PSRR) for voltage regulators the regulator can be supplied by its own regulated voltage. This configuration needs a dedicated startup circuit to start the operation of the circuit. Common practice for the implementation of a startup circuit is to apply the startup condition as long as the output voltage of the regulator is below a certain voltage. This practice requires some voltage reference for the startup circuit and does not account for process variations. Therefore the switch-off voltage of the startup condition has to be chosen for worst case conditions to guarantee startup. This limits the output voltage range of the regulator output at the low voltage end.
This invention solves several problems associated with the related art by disclosing a self-supplied voltage regulator circuit that does not need a voltage reference for startup, is process independent, has a wider regulator output voltage range for low voltages and where the startup is always switched off at the lowest possible output voltage.
U.S. Patents which relate to the subject of the present invention are:
U.S. Pat. No. 4,051,392 (Rosenthal et al.) discloses a circuit of current amplifiers including startup circuitry.
U.S. Pat. No. 4,333,047 (Flink) discloses a current control circuit that can be used starting current during buildup of an input voltage.
U.S. Pat. No. 4,476,428 (Iwaswa et al.) discloses a power supply device comprising a reference voltage generator and a constant current circuit to create a reference voltage and a startup circuit to supply starting current to the constant current circuit.
U.S. Pat. No. 4,567,426 (van de Plassche et al.) discloses a current stabilizer with a starting circuit.
U.S. Pat. No. 4,740,742 (Gontowski, Jr.), identified by inventor, discloses a startup circuit for voltage regulator with a first and second current mirror circuit responsive to a voltage output.
U.S. Pat. No. 5,612,641 (Sali) discloses a circuit for setting initial conditions when starting up and integrated circuit device.
U.S. Pat. No. 5,666,044 (Tuozzolo), identified by the inventor, discloses a circuit providing startup capability and foldback protection to a voltage regulator.
U.S. Pat. No. 5,742,155 (Susak et al.) discloses a zero current startup circuit for a reference circuit that is initially unbiased and has internal nodes that need to be regulated.
U.S. Pat. No. 5,969,549 (Kim et al.) discloses a current detection startup circuit used to restart a reference voltage circuit.
U.S. Pat. No. 6,963,191 B1 (McCalmont) discloses a reference circuit using a low threshold FET for improved startup operation.
U.S. Pat. No. 7,265,529 B2 (Nazarian) discloses a startup circuit and method for self bias circuits to initialize operations in a stable state.
U.S. Pat. No. 7,436,244 B2 (Lin) discloses a reference circuit for reference current used in voltage generation wherein a current bias circuit provides a startup signal.
U.S. Pat. No. 7,477,532 B2 (Hall et al.) discloses a startup controller for a PWM power supply controller that is substantially independent of temperature and changes in output voltage.
U.S. Pat. No. 7,583,070 B2 (Nazarian) discloses a startup circuit for self bias circuits that provides a startup voltage and current to initialize operations in a stable state.
U.S. Patent Application Publication 2005/0077933 (Sukup et al.) discloses a power control system using separate current to control startup operation.
U.S. Patent Application Publication 2009/0021229 A1 (Heilmann) discloses a method and apparatus for enabling a voltage regulator wherein a startup circuit is connected to a bias network to assist the bias network to set an amplifier bias current during a startup time period.
It should be noted that none of the above-cited examples of the related art provide the advantages of the below described invention.